Federal magistrate judge in Illinois rules that being forced to unlock your phone with a fingerprint could violate your rights

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M. David Weisman, a magistrate judge in Illinois's Eastern Division, denied a federal warrant application that would have allowed law enforcement officers to force suspects to unlock their mobile devices with a fingerprint, ruling that the suspects' Fourth Amendment (undue search and seizure) and Fifth Amendment (self-incrimination) rights protected them from being forced to unlock their devices.

This is significant in part because of an emerging legal consensus that the Fifth Amendment -- which protects US persons from being forced to testify against themselves -- didn't extend to using a fingerprint to unlock their devices. The thumbnail sketch of this argument is "The Fifth protects you from being forced to disclose something you know, but not from being forced to surrender something you have. Your fingerprint is something you have. If we said that being forced to give up fingerprints violated the Fifth, we'd also have to include other forms of evidence gathered from your body, like breathalyzers."

Judge Weisman formerly served as a federal prosecutor and an FBI agent, and is thus presumably sympathetic to the needs of working law enforcement and prosecutorial personnel, but he nevertheless wrote that, "This Court agrees that the context in which fingerprints are taken, and not the fingerprints themselves, can raise concerns under the Fourth Amendment. In the instant case, the government is seeking the authority to seize any individual at the subject premises and force the application of their fingerprints as directed by government agents."

Weisman's ruling leaves the Fifth Amendments limitations -- and thus breathalyzers -- intact, but instead invokes the Fourth Amendment, which protects you against overbroad "search and seizure." The Fourth isn't implicated when your fingerprints are taken for the purpose of criminal identification, but when the same process is used to get access to enormous amounts of potentially irrelevant, personal, sensitive information about you and the people in your social network and email archives, the Fourth comes into play.

Magistrate judges -- even federal ones -- are pretty low on the judicial totem pole, and there are many higher courts that could reverse Weisman. Nevertheless, his gloss on this complicated issue is making a stir in privacy law circles, and suggests that the government's usual legal theory for compelling the unlocking of phones is alarming to the kinds of judges from whom they seek routine warrants.

Warrant applications like this one are often sealed and are issued without public scrutiny, so we don't really know how often these arguments are raised.

One important note: the Fifth almost certainly protects you from being forced to unlock your phone with a passcode -- it's something you know, not something you have -- so you can avoid the whole mess by switching to PINs instead of fingerprints, though this leaves you with the unhappy tradeoff between a long, strong passcode and the need to frequently unlock your devices.

"As I read the opinion, the government relies on old fingerprinting cases to argue that the Fourth and Fifth Amendments don’t stand in the way of what they are seeking to do here," Abraham Rein, a Philadelphia-based tech lawyer, told Ars by e-mail.

"But (as the court points out) there is a big difference between using a fingerprint to identify a person and using one to gain access to a potentially vast trove of data about them and possibly about innocent third parties, too. The old fingerprinting cases aren’t really good analogs for this new situation. Same is true with old cases about using keys to unlock locks—here, we’re not talking about a key but about part of a person’s body."

Orin Kerr, a well-known privacy and tech law expert and a professor at George Washington University, told Ars that the judge had largely reached the right result, but only on Fourth Amendment, and specifically not Fifth Amendment grounds.

"I just think that it's really clear that [fingerprints are] not testimonial—because you’re not using your brain," he said. "It can’t be testimonial if you can cut their finger off."

Similarly, Paul Rosenzweig, an attorney and former Homeland Security official, argued that it’s essentially impossible for a fingerprint, even a digital fingerprint, to have any Fifth Amendment implications.

"We could have gone down the road of saying that providing physical evidence is testimony against yourself," he said. "But we long ago made the decision that the Fifth Amendment applied to testimony, and testimony meant only oral utterances or other things that conveyed a message. For this distinction lies at the core of Breathalyzer tests. If we roll that back, Breathalyzer tests go out the window. Blowing your air would be testifying against yourself."

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